U.S. patent number 7,182,867 [Application Number 11/043,370] was granted by the patent office on 2007-02-27 for shear-enhanced systems and methods for removing waste materials and liquid from the blood.
This patent grant is currently assigned to Baxter International Inc.. Invention is credited to Gretchen Kunas, Julie Moriarty, Rohit Vishnoi.
United States Patent |
7,182,867 |
Moriarty , et al. |
February 27, 2007 |
Shear-enhanced systems and methods for removing waste materials and
liquid from the blood
Abstract
Systems and methods convey the blood through a gap defined
between an inner surface that is located about an axis and an outer
surface that is concentric with the inner surface. At least one of
the inner and outer surfaces carries a membrane that consists
essentially of either a hemofiltration membrane or a hemodialysis
membrane. The systems and methods cause relative movement between
the inner and outer surfaces about the axis at a selected surface
velocity, taking into account the size of the gap. The relative
movement of the two surfaces creates movement of the blood within
the gap, which creates vortical flow conditions that induce
transport of cellular blood components from the membrane while
plasma water and waste material are transported to the membrane for
transport across the membrane. Shear-enhanced transport of waste
materials and blood plasma water results.
Inventors: |
Moriarty; Julie (Evanston,
IL), Vishnoi; Rohit (Deerfield, IL), Kunas; Gretchen
(Pleasanton, CA) |
Assignee: |
Baxter International Inc.
(Deerfield, IL)
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Family
ID: |
27658662 |
Appl.
No.: |
11/043,370 |
Filed: |
January 26, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050133448 A1 |
Jun 23, 2005 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10066311 |
Feb 2, 2002 |
6863821 |
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Current U.S.
Class: |
210/321.68;
210/321.67; 210/321.78; 210/360.1; 210/645; 210/646; 210/650 |
Current CPC
Class: |
A61M
1/16 (20130101); A61M 1/342 (20130101); B01D
61/145 (20130101); B01D 61/18 (20130101); B01D
61/28 (20130101); B01D 63/06 (20130101); B01D
63/16 (20130101); B01D 65/08 (20130101); A61M
1/262 (20140204); A61M 1/265 (20140204); A61M
1/3417 (20140204); A61M 1/3437 (20140204); A61M
1/3458 (20140204); B01D 2321/2033 (20130101); B01D
2321/2041 (20130101); B01D 2321/205 (20130101) |
Current International
Class: |
B01D
63/16 (20060101); B01D 61/14 (20060101); B01D
61/00 (20060101); B01D 63/00 (20060101) |
Field of
Search: |
;210/645,646,650,321.67,321.68,321.78,360.1 |
References Cited
[Referenced By]
U.S. Patent Documents
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WO 85/04112 |
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Sep 1985 |
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WO |
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Primary Examiner: Menon; Krishnan S.
Attorney, Agent or Firm: Price; Bradford R. L. McFarron;
Gary W.
Parent Case Text
RELATED APPLICATION
This application is a continuation of application Ser. No.
10/066,311, filed on Feb. 2, 2002, now U.S. Pat. No. 6,863,821 and
entitled "Shear-Enhanced Systems and Methods for Removing Waste
Materials and Liquids from the Blood."
Claims
We claim:
1. A system for removing waste from the blood of an individual
comprising an access device for withdrawing blood from an
individual; a blood processing device, including an inlet; a first
flow path in fluid communication between said access device and
said inlet for conveying whole blood from the individual to said
blood processing device; said blood processing device comprising a
gap defined between an inner surface that is located about an axis
and an outer surface that is concentric with the inner surface,
said inlet and a first outlet communicating with the gap for
continuous flow of blood between the inlet and the first outlet, at
least one of the inner and outer surfaces carrying a hemofiltration
membrane having one surface facing the gap and another surface
facing away from the gap and said membrane having a pore size
sufficiently small to prevent passage of molecules greater than
about 50,000 Daltons so as to prevent the passage of albumin, a
driver causing relative movement between the inner and outer
surfaces about the axis at a selected surface velocity, taking into
account the size of the gap, to create movement of the blood within
the gap that induces transport of cellular blood components from
the membrane while plasma water and waste material are transported
to the membrane for transport across the membrane; a second flow
path in fluid communication with the first outlet for conveying
blood components from said processing device for return to the
individual; a second outlet communicating with the membrane surface
facing away from the gap; and a third flow path in communication
with said second outlet for conveying plasma water and waste
material away from said blood processing device.
2. A system according to claim 1 wherein the hemofiltration
membrane includes a first surface facing toward the gap and a
second surface facing away from the gap, and wherein the blood
processing device includes a channel along the second surface of
the hemofiltration membrane to convey waste material transported
across the hemofiltration membrane.
3. A system according to claim 1 wherein the drive mechanism
rotates the inner surface while holding the outer surface
stationary.
4. A system according to claim 1 wherein the drive mechanism
rotates the inner surface at a higher rate of rotation than the
outer surface.
5. A system according to claim 1 wherein the other of the inner and
outer surfaces carry a membrane that consists essentially of at
least one of a hemofiltration membrane and a hemodialysis
membrane.
6. A system according to claim 5 wherein both surfaces carry a
hemofiltration membrane.
7. A method for removing waste from the blood of an individual
comprising the steps of continuously conveying blood from an
individual through a first flow path communicating between such
individual and an inlet into a gap defined between an inner surface
that is located about an axis and an outer surface that is
concentric with the inner surface, at least one of the inner and
outer surfaces carrying a hemofiltration membrane having one
surface facing the gap and another surface facing away from the gap
and having a pore size sufficiently small to prevent passage of
molecules greater than about 50,000 Daltons so as to prevent the
passage of albumin, causing relative movement between the inner and
outer surfaces about the axis at a selected surface velocity,
taking into account the size of the gap, to create movement of the
blood within the gap that induces transport of cellular blood
components from the membrane through the gap while plasma water and
waste material are transported to the membrane for transport across
the membrane; returning blood components to the individual through
a second flow path in fluid communication between the gap and said
individual, and conveying the plasma water and waste material
through a third flow path in fluid communication with the surface
of the membrane facing away from the gap.
8. A method according to claim 7 further including the step of
conveying away material that is transported across the
hemofiltration membrane.
9. A method according to claim 7 wherein the inner surface is
rotated while holding the outer surface stationary.
10. A method according to claim 7 wherein the inner surface is
rotated at a higher rate of rotation than the outer surface.
11. A method according to claim 7 wherein the other of the inner
and outer surfaces carry a membrane that consists essentially of at
least one of a hemofiltration membrane or a hemodialysis
membrane.
12. A method according to claim 11 wherein both surfaces carry a
hemofiltration membrane.
Description
FIELD OF THE INVENTION
This invention relates to systems and methods that remove waste
materials and liquid from the blood of an individual whose renal
function is impaired or lacking.
BACKGROUND OF THE INVENTION
For various reasons, including illness, injury or surgery, patients
may require replacement or supplementation of their natural renal
function in order to remove excess fluid or fluids containing
dissolved waste products from their blood. Several procedures known
for this purpose are hemodialysis, hemofiltration,
hemodiafiltration and ultrafiltration.
SUMMARY OF THE INVENTION
The invention provides shear-enhanced systems and methods for
removing waste materials and liquid from the blood.
The systems and methods convey the blood through a gap defined
between an inner surface that is located about an axis and an outer
surface that is concentric with the inner surface. At least one of
the inner and outer surfaces carries a membrane that consists
essentially of either a hemofiltration membrane or a hemodialysis
membrane. The systems and methods cause relative movement between
the inner and outer surfaces about the axis at a selected surface
velocity, taking into account the size of the gap. The relative
movement between the inner and outer surfaces creates movement of
the blood within the gap, which creates a vortical flow condition
that induces transport of cellular blood components from the
membrane while plasma water and waste material are transported to
the membrane for transport across the membrane.
The circulatory forces of the vortical flow condition clear the
membrane surface of occluding cellular components to maintain
efficient operation. The circulatory forces also supplement the
shear forces exerted on the blood by viscous drag. Due to the
circulatory forces, the concentration of waste materials in the
blood plasma water becomes more homogenous. As a result, the
transport of waste materials and associated blood plasma water
across the membrane is significantly enhanced. Shear-enhanced waste
removal makes possible the use of smaller processing devices and/or
processing at reduced blood flow rates.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a system that includes a blood
processing unit for removing waste material and plasma water from
the blood;
FIG. 2 is a side section view of one embodiment of a blood
processing unit that the system shown in FIG. 1 can incorporate for
the purpose of performing shear-enhanced hemofiltration;
FIG. 3 is a side section view of another embodiment of a blood
processing unit that the system shown in FIG. 1 can incorporate for
the purpose of performing shear-enhanced hemodialysis;
FIG. 4 is a side section view of another embodiment of a blood
processing unit that the system shown in FIG. 1 can incorporate for
the purpose of performing shear-enhanced hemodialysis;
FIG. 5 is a side section view of another embodiment of a blood
processing unit that the system shown in FIG. 1 can incorporate for
the purpose of performing shear-enhanced hemofiltration and
hemodialysis;
FIG. 6 is an enlarged and simplified perspective view of a gap
formed between a stationary and rotating concentric surfaces, of a
type that the blood processing units shown in FIGS. 2 to 5
incorporate, in which vortical flow conditions provide
shear-enhanced waste material and plasma water removal; and
FIG. 7 is an enlarged side sectional view of the vortical flow
conditions shown in FIG. 5 that provide shear-enhanced waste
material and plasma water removal.
The invention may be embodied in several forms without departing
from its spirit or essential characteristics. The scope of the
invention is defined in the appended claims, rather than in the
specific description preceding them. All embodiments that fall
within the meaning and range of equivalency of the claims are
therefore intended to be embraced by the claims.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a system 10 for removing waste material (e.g., urea,
creatinine, and uric acid) and plasma water from the blood of an
individual whose renal function is impaired or lacking. The system
10 includes a blood processing unit 12 that receives whole blood
from the individual. The individual typically has one or more
surgically installed vascular access devices, such as an
arterial-venous fistula, to facilitate coupling the blood
processing unit 12 to the circulatory system of the individual. In
the illustrated embodiment, arterial whole blood is drawn from the
individual through an inlet path 14. An inlet pump 16 governs the
blood inlet flow rate.
The blood processing unit 12 includes a membrane 18, along which
the whole blood drawn from the individual is conveyed. The membrane
18 can have different functional and structural characteristics,
which affect the manner in which waste material is transported by
the membrane 18. Generally speaking, waste material carried in
blood plasma water can be separated by the membrane 18 from the
whole blood either by convective transport, which is driven by
pressure differentials across the membrane (in a process known as
hemofiltration), or by diffusion, which is driven by concentration
gradients across the membrane (in a process known as hemodialysis).
The waste materials and associated blood plasma water are removal
from the blood processing unit 12 through a waste path 20 for
discard.
The pores of the membrane 18 desirably have a molecular weight
cut-off that block the passage of cellular blood components and
larger peptides and proteins (including albumin) across the
membrane. These components are retained in the blood, which is
conveyed from the blood processing unit 12 through an outlet path
22 for return to the individual. In the illustrated embodiment, the
treated blood is returned to the venous blood circulatory system of
the individual.
Fresh physiologic fluid, called replacement fluid, is typically
supplied from a source 24 to the plasma water and toxin-depleted
blood. The replacement fluid restores, at least partially, a normal
physiologic fluid and electrolytic balance to the blood returned to
the individual.
The relative volumes of waste plasma water removed and replacement
fluid supplied can be monitored, e.g., by gravimetric means, so
that a desired volumetric balance can be achieved. An
ultrafiltration function can also be performed by the blood
processing unit 12, by which plasma water is replaced in an amount
slightly less than that removed. Ultrafiltration decreases the
overall fluid level of the individual undergoing treatment, which
typically increases due to normal fluid intake between treatment
sessions.
The blood processing unit 12 includes a processing cartridge 26, in
which the membrane 18 is housed. The cartridge 26 is desirable
disposable and, in one representative embodiment (see FIG. 2),
includes a generally cylindrical housing 28, which is sized to be
conveniently manipulated by an operator. The housing 28 can be
oriented for use either horizontally or vertically, or any
intermediate position.
An elongated cylindrical rotor 30 (which can also be called a
"spinner") is rotatably supported within the housing 28 between
oppositely spaced pivot bearings 32 and 34. The rotor 30 rotates
within the housing 28, which is held stationary during use.
However, other manners of operation are possible, and the housing
need not be held stationary.
An annular gap 36 is formed between the outer surface of the rotor
30 and the interior wall 38 of the housing 28. Whole blood in the
inlet path 14 is conveyed through a blood inlet port 40 into the
gap 36 for processing by the inlet pump 16. After processing, the
blood is discharged from the gap 36 through an oppositely spaced
outlet port 42, which communicates with the blood return path
22.
In the illustrated embodiment, a magnetic drive assembly 44
provides rotation to the rotor 30. A ring of magnetic material 46
in the rotor 30 is acted upon by a rotating magnetic field
generated by an external, rotating magnetic drive member 48, which
releasably engages the adjacent end of the housing 28 for use. The
rotor 30 rotates relative to the stationary interior wall 38 of the
housing 28. The magnetic drive member 48 rotates the rotor 30 at a
predetermined angular velocity.
Further details regarding devices employing a spinning rotor and a
stationary housing for blood filtration can be found in U.S. Pat.
No. 5,194,145 and U.S. Pat. No. 4,965,846, which are incorporated
herein by reference.
Further details of construction and operation of the processing
cartridge 26 can differ, depending upon the type of blood
processing sought to be performed. If hemofiltration is to be
performed, the membrane 18 comprises an appropriate hemofiltration
membrane (as FIG. 2 shows). If hemodialysis is to be performed, the
membrane 18 comprises an appropriate hemodialysis membrane (as
FIGS. 3 and 4 show). If hemodialysis with hemofiltration is to be
performed, the processing cartridge 26 can include both a
hemofiltration membrane and a hemodialysis membrane (as FIG. 5
shows).
A. Hemofiltration
In the embodiment shown in FIG. 2, the rotor 30 has an internal
cavity 50 bounded by a grooved cylindrical wall 52 forming a
network of channels 56. A hemofiltration membrane 54 covers the
outer surface of grooved wall 52. The hemofiltration membrane 54
can comprise, e.g., a biocompatible synthetic material such as
polysulfone, polyacrylonitrile, polymethylmethacrylate,
polyvinyl-alcohol, polyamide, polycarbonate, etc., and cellulose
derivatives. The pores of hemofiltration membrane 54 desirably
allow passage of molecules up to about 30,000 Daltons, and
desirably not greater than about 50,000 Daltons, to avoid the
passage of albumin (molecular weight of 68,000 Daltons).
The network of channels 56 convey blood plasma water passing
through the membrane 54 into the cavity 50. An outlet port 58
communicates with the cavity 50 to convey blood plasma water from
the processing cartridge 26.
In operation, as the rotor 30 is rotated, the pump 16 conveys whole
blood into the gap 36. The whole blood flows within the gap 36 in
contact with the hemofiltration membrane 54.
In response to the transmembrane pressure created by the pump 16,
waste material and associated blood plasma water flow from the gap
36 through membrane 54 into the channels 56. Waste material and
associated blood plasma water are discharged from the processing
cartridge through the outlet port 58. Cellular blood components
continue to flow within the gap 36 for discharge through the outlet
port 42.
It should be appreciated that, alternatively, the hemofiltration
membrane 54 can be mounted on the stationary wall 38 of the housing
28, instead of being mounted on the spinning rotor 30, as FIG. 2
shows. In this arrangement, the network of channels 56
communicating with the waste outlet port 58 would be formed in the
stationary wall 38, and the membrane 54 would overlay the channels
in the same fashion shown in FIG. 2. It should also be appreciated
that, alternatively, a hemofiltration membrane 54 can be mounted on
both the spinning rotor 30 and the stationary wall 28 and used in
tandem for waste material and plasma water removal.
B. Hemodialysis
In the embodiment shown in FIG. 3, the interior wall 38 of the
housing 28 has a network of channels 60 communicating with an inlet
port 62 and an outlet port 64. A semipermeable hemodialysis
membrane 66 overlays the network of channels 60. The membrane 66
can, e.g., comprise a medium to high flux membrane, for example, a
polysulfone, cellulose triacetate or acrylonitrile membrane. Such
membranes are typically well suited to fluid and small solute (less
the 10,000 Daltons) removal. One side of the membrane 66 faces the
annular gap 36 and the rotor 30, which, in the illustrated
embodiment, carries no membrane. The other side of the membrane 66
faces the channels 60.
In operation, as the rotor 30 is rotated, the pump 16 conveys whole
blood into the gap 36. The whole blood flows within the gap 36 in
contact with membrane 66. Fresh dialysate is circulated by a pump
70 from a source 68 through the channels 60 via the ports 62 and
64. Desirably (as FIG. 3 shows), the dialysate is circulated
through the channels 60 in a flow direction opposite to the
direction of whole blood flow in the gap 36.
As blood flows through the gap 36, plasma water is conveyed across
the membrane 66 due to transmembrane pressure created by the pump
16. Targeted waste materials are also transferred across the
membrane 66 by diffusion, due to a difference in concentration of
these materials in the blood (high concentrations) and in the fresh
dialysate (low concentrations). In response to the high-to-low
concentration gradient, waste materials flow from the gap 36
through the membrane 66 into the dialysate. The waste materials are
discharged with the spent dialysate out of the processing cartridge
26 to, e.g., a drain. Cellular blood components continue to-flow
within the gap 36 for discharge through the outlet port 42 for
return to the individual.
As shown in FIG. 4, in an alternative embodiment, the rotor 30 can
include a network of channels 72 through which dialysate can be
circulated in the manner just described. In this arrangement, a
hemodialysis membrane 74 overlays the network of channels 72 on the
rotor 30. One side of the membrane 74 faces the annular gap 36. The
other side of the membrane faces the channels 72.
It should be appreciated that the hemodialysis membrane 74 on the
rotating rotor 36 can also be used in combination with the
hemodialysis membrane 66 on the stationary interior wall 38 of the
housing 28, or by itself (in which case the stationary interior
wall 38 of the housing 28 would be free of a membrane.
As shown in FIG. 5, the processing cartridge 26 can include a
hemodialysis membrane 66 mounted on either the rotor 30 or the
interior housing wall 38 and a hemofiltration membrane 54 mounted
on the other location. In this arrangement, the processing
cartridge 26 accommodates hemdialysis with hemofiltration, a
process also called hemodiafiltration.
C. Shear-Enhanced Waste Removal
In an annular gap 36 as just described, which is defined between
two concentric surfaces (e.g., the rotor 30 and the interior
housing wall 38), rotation of the inner surface relative to the
outer surface can induce vortical flow conditions in the blood
residing in the gap 36. The vortical flow conditions take the form
of successive, alternately circulating, annuli TV (see FIG. 6) in
the gap 36 between the two concentric surfaces. This vortex action
can be a type that can be generally classified as "Taylor vortices"
(as designated as TV in FIG. 6). The nature of the Taylor vortices
can vary among laminar stable Taylor vortices, wavy non-stable
Taylor vortices, turbulent Taylor vortices, or other intermediate
vortical flow conditions.
Taylor vortices will develop in the blood occupying the gap 36,
regardless of whether the membrane is mounted on the inner surface
or on the outer surface, or both surfaces. Taylor vortices develop
in the blood occupying the gap 36 as a result of relative movement
between the inner and outer surfaces, regardless of whether one of
the surfaces is held stationary while the other rotates, or whether
both surfaces are allowed to rotate. To achieve desired vortical
flow conditions, it is believed that the inner surface should be
rotated relative to the outer surface, and, if the outer surface is
allowed to rotate, the rate of rotation of the inner surface should
exceed the rate of rotation of the outer surface.
The amplitude of the vortex action, which is characterized by the
Taylor number, is a function of the rate of rotation of the
rotating surface and the radial dimension of the gap 36. At a given
radial dimension, increasing the rate of rotation will increase the
amplitude of the vortex action, leading to a higher Taylor number.
Given a rate of rotation, narrowing the radial dimension of the gap
36 will also increase the amplitude vortex action, leading to a
higher Taylor number. It is believed that radial dimension of the
gap 36 and the rate of rotation should be selected to yield a
Taylor number that is greater than the critical Taylor number, at
which vortical flow conditions develop.
Transmembrane pressure is also desirably monitored and maintained
(by controlling operation of the pump 16) at a magnitude that
maximizes fluid transport across the membrane without driving
cellular blood components into the membrane pores, which can cause
membrane plugging, hemolysis, and trauma to fragile cellular blood
components residing within the gap 36.
When maintained within desired limits, the vortical flow conditions
provide a sweeping action in the gap 36 (see FIG. 7) that
transports cellular blood components away from the membrane while
blood plasma water carrying the targeted uremic toxins is
transported to the membrane for passage through the pores of the
operative membrane. The circulation caused by the vortical flow
conditions removes adherent cellular blood components from the
surface of the operative membrane and replenishes available blood
plasma water for transport through the membrane pores. The vortical
flow conditions thereby clear the membrane surface of occluding
cellular components to maintain efficient operation at desirable
transmembrane pressure levels. The circulatory forces also
supplement the shear forces exerted on the blood by viscous drag,
which is tangential to the spinning membrane surface. Furthermore,
due to the circulatory forces, the concentration of waste materials
in the blood plasma water becomes more homogenous. In all, the
transport of waste materials and associated blood plasma water
across the membrane is significantly enhanced. Shear-enhanced waste
removal makes possible the use of smaller processing devices and/or
processing at reduced blood flow rates.
If desired, ultrafiltration volume can be augmented by placing,
either upstream or downstream of the processing cartridge 26, an
auxiliary processing cartridge 76 (shown in phantom lines in FIG.
1). The auxiliary processing cartridge 76 subjects the blood to
plasma water removal (either by hemodialysis or hemofiltration) in
addition to the plasma water removal by the processing cartridge
26. An auxiliary processing cartridge 76 can also be used in series
with the processing cartridge 26, to provide waste removal by
hemofiltration to augment waste removal by hemodialysis conducted
by the processing cartridge 26, or vice versa.
Various features of the invention are set forth in the following
claims.
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